Leaving aside the fact that justification still doesn’t work that well on the web, I’m scratching my head as to why you’d really want to do it. True, it looks a little neater than left aligned text, but I can’t see any readability benefits (quite the opposite). Words are meant to be read, not just looked at.
I’d guess that justification works in print because its a lot easier to fine tune spacing and therefore hyphenation. And there’s no chrome to distract you from the text itself. But neither apply to web pages.